Alternative conifer release treatments affect microclimate and soil nitrogen mineralization Phillip E. Reynolds a,* , Naresh V. Thevathasan b , James A. Simpson b , Andrew M. Gordon b , R.A. Lautenschlager c , Wayne F. Bell c , Donald A. Gresch b , Donald A. Buckley b a Natural Resources Canada, Canadian Forest Service, 1219 Queen St. East, Sault Ste. Marie, Ont., Canada P6A 5M7 b Department of Environmental Biology, University of Guelph, Guelph, Ont., Canada N1G 2W1 c Ontario Ministry of Natural Resources, Ontario Forest Research Institute, 1235 Queen St. East, Sault Ste. Marie, Ont., Canada P6A 5N5 Accepted 6 October 1999 Abstract In 1993, the Fallingsnow Ecosystem Project was initiated in northwestern Ontario to assess the effects of alternative conifer release practices on ecosystem processes, wildlife populations, and spruce production. Conifer release treatments: two herbicide (glyphosate and triclopyr), two cutting treatments (brushsaw and Silvana selective mower), and controls were established on four 30±60 ha clearcut and planted (spruce) blocks. Unharvested controls adjacent to each block constituted a sixth treatment. Objectives of this study were: (1) to quantify soil nitri®cation rates for the control, glyphosate, brushsaw, and unharvested forest treatments and (2) to relate these rates to soil temperature and moisture. Weather stations and buried ®berglass/resistance soil cells were established in 1994 to monitor soil temperatures and moisture. During the second posttreatment growing season (1995), soil samples were collected at 5, 15, and 30 cm depth and incubated in polyethylene bags at the same depth from which they were collected for 30 days prior to exhumation. The above procedure was repeated for the months of June, July, August, and September. In the third posttreatment growing season (1996), bags were buried (mid- June, mid-July, mid-August) at 5 cm only and exhumed 30 days after burial. Higher levels of nitrate (NO 3  ) were observed for the glyphosate and brushsaw treatments in August 1995 compared with the control and unharvested forest treatments. Rates (mg 100 g 1 dry soil per day) of ammonium (NH 4  ) and nitrate production decreased with soil depth and exhibited a distinctive seasonal trend, decreasing as soil temperatures declined. Ammonium production was signi®cantly correlated with soil temperature and moisture, increasing with increasing temperature, and decreasing at higher moisture levels. By the third (1996) posttreatment growing season, no treatment-related differences were observed, and ammonium production was less correlated with soil temperature than during the second (1995) posttreatment growing season. These results af®rm that application of glyphosate is the best option evaluated for effective weed control and optimal nutrient release. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Fallingsnow Ecosystem project; Soil nitrogen mineralization; Alternative conifer release treatments; Glyphosate; Brushsaw cutting; Vegetation management; Harvesting; Forestry practices; Ecosystem processes; Microclimate Forest Ecology and Management 133 (2000) 115±125 * Corresponding author. Tel.: 1-705-949-9461. E-mail address: preynold@nrcan.gc.ca (P.E. Reynolds) 0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII:S0378-1127(99)00302-3